1. FIELD OF THE INVENTION
The present invention relates to a method of and a device for analyzing one ingredient in a mixed solution with two light beams of different wavelengths, and more particularly to an analytical method and instrument suitable for the analysis of an ingredient whose absorption spectrum is unknown in a mixed solution containing more than two kinds of ingredient.
2. DESCRIPTION OF PRIOR ART
The method of and device for analyzing one ingredient in a mixed solution with two light beams of different wavelengths have been proposed in a Japanese Patent Application (Publication No. 44224/77) entitled "Separate and quantitative analysis employing two-wavelength spectrophotometer", and in a Japanese Patent Application (Laid-open No. 91483/77) entitled "Apparatus for analysing one ingredient in a multi-ingredient mixture" which corresponds to a copending U.S. Patent Application Ser. No. 763,674, now U.S. Pat. No. 4,136,959.
The Japanese Patent Application (Publication No. 44224/77) discloses a method of separate and quantitative analysis employing a two-wavelength spectrophotometer such that, in order to determine one ingredient in a mixed solution, any two wavelengths are selected in an absorption spectrum of another ingredient, the wavelengths of the two-wavelength spectrophotometer are set at the selected ones, and an output signal due to another ingredient at one of the set wavelengths is multiplied by a selected factor to be made equal to an output signal due to another ingredient at the other of the set wavelengths, that is, to make a difference absorbance indicated by the spectrophotometer equal to zero, thereby eliminating the disturbance by another ingredient.
The Japanese Patent Application (Laid-open No. 91483/77) teaches an analytical apparatus for directly determining a desired ingredient independently of a coexisting ingredient in which two light beams of different wavelengths pass through a mixture to produce respective photometric signals, the signals are subjected to logarithmic conversion to deliver respective output signals, and the output signals are multiplied by respective factors which make the difference of absorbances due to the coexisting ingredient alone at the two wavelengths equal to zero, to obtain a difference between the output signals thus modified.
The above-mentioned patent applications disclose only a method of and apparatus for determining one ingredient in a mixture containing ingredients, the absorption spectrum of each of which is known , and never teach nor suggest the qualitative analysis or identification of that ingredient contained in a mixture whose absorption spectrum is unknown.
In a medical institution such as a hospital, there is often found such a case that, when a mixture containing ingredients whose absorption spectra are all known is left at rest for a time, the mixture is converted into a different mixture containing an ingredient whose absorption spectrum is unknown. Therefore, it is earnestly required to accomplish a method and apparatus capable of qualitatively indicating what kind of ingredient has been produced with the passage of time. However, an appropriate method and/or apparatus which can satisfy the above-mentioned requirement have not yet been proposed.
Further, it is very difficult to identify or qualitatively determine one ingredient whose absorption spectrum is unknown in a mixture by the method and apparatus described in the above-mentioned Japanese Patent Applications for the following reasons. In order to identify the ingredient having an unknown absorption spectrum, it is necessary to obtain a difference-absorbance spectrum of the ingredient by such a method as fixing one of the measuring wavelengths and varying the other. However, in the method and apparatus according to the Japanese Patent Applications, the factors, by which two photometric signals are multiplied, are so adjusted as to make a difference-absorbance of a coexisting ingredient with respect to two specified wavelengths equal to zero. That is, the optical and electrical conditions are selected and fixed with respect to the specified two wavelengths. Accordingly, it is not possible to scan a sample with the wavelength of light in the abovementioned method and apparatus.